Yang Hao Design Institute of Coal Industry Hefei Power Plant, Hefei 230041 Institute of Electric Power in the design of the primary and secondary electrical equipment selection are discussed. 1 Principles for selection of electrical equipment The 10kV substation is an important part of the internal power supply and distribution system of industrial and mining enterprises. It consists of allocating one or two 10kV power supplies into multiple 10kV power supplies and sending them to other power usage points via the line. Also includes 10/0.4kV substation power distribution section. An important link in the design of 10kV substations is the selection of primary and secondary electrical equipment. The principle is that it should be easy to install and maintain. It can meet the requirements of normal operation in the local environment and can meet the requirements of short circuit and over-voltage and meet the requirements of 10kV. The following substation design specifications (GB50053-94) and other specification requirements, and follow the following principles. Select the rated voltage and rated current according to the normal working conditions; verify the dynamic stability and thermal stability of the electrical equipment according to the short-circuit condition; verify the breaking capacity of the high-voltage circuit breaker according to the three-phase short-circuit capacity of the device location. Almost 10kV substations all use switchgear cabinets. High-voltage switchgears can be divided into fixed and removable ones according to their structure. There are mainly KGN and XGN series in the fixed switchgear; the switchgear mainly includes YN and KYN series. The code name of the removed or handcart type cabinet is indicated by a capital letter Y: The main electrical components in the cabinet are installed on the extractable handcart, and the handcart cabinet has a good interchangeability, which can greatly improve the reliability of power supply. Sex. The feature of armored handcart cabinets is that the cabinet type adopts the building block type structure. The switchgear cabinet is composed of a handcart room, a bus room, a cable room and a relay meter room. This type of cabinet has the advantages of convenient and safe maintenance, high reliability of power supply, and can meet the “five prevention†functional requirements that high-voltage switchgear should have. Fixed cabinets are indicated with a capital letter G: All the electrical components in the cabinet are fixed, and the fixed switchgear is relatively simple and economical. Its characteristic is that the number of compartments is less than the armored type and spacing type, the protection level of the board cannot reach the specified requirements, the structure is simple, and the representative product is the XGN series. In the light of the characteristics of various cabinets and the conditions during operation, the author believes that 10kV substations are recommended to use removable and armored cabinets. The selection of power transformers should be based on factors such as the characteristics of electricity load, economic operating conditions, energy saving, and the reduction of project cost. Transformers are divided into two major categories: oil immersed and dry. The main products of oil-immersed transformers are S7, SL7, SF7, SZL7, and S9 series. Compared with the S7 series, S9 series transformers reduce the no-load loss by 8% and the load loss by about 25%. The S11 series of transformers is based on the S9 series to improve the structural design, the use of ultra-thin silicon steel sheet, no-load losses further reduced, the current no-load loss of the S11 series of transformers than the S9 series reduced by 30%, but the investment is relatively high. The main products of dry-type transformers are the SC series. These transformers have the advantages of flame resistance, dust resistance, moisture resistance, small partial discharge, and good seismic performance. Dry-type transformers are mainly classified into two types: impregnated dry-type transformers and resin dry-type transformers. Impregnated dry-type transformers are mostly used in hydropower stations and high-rise buildings and have good fire resistance. Transformer insulation is divided into B, F, H, C grade. This kind of transformer is influenced by the environment more than the resin type dry type transformer, appearance and weight are also large, the output at home and abroad tends to reduce. The resin dry-type transformer design and pouring process is scientific and reasonable. The coil is encapsulated by epoxy resin and has the advantages of flame retardant, fireproof, explosion-proof, maintenance-free, non-pollution, and small size. It can be directly installed in the load center. The resin-type dry-type transformer has smaller partial discharge, low noise, and strong heat dissipation capability. Under forced air-cooling conditions, it can operate under a 125% rated load for a long period of time. Under normal circumstances, priority should be given to the use of low-loss transformers such as S9 and S11. If the surrounding environment is harsh, fully sealed power transformers BS7 and BS9 with dust-proof and anti-corrosion properties should be used. For high-rise buildings, underground railways, tunnels, airports and other places with high fire protection requirements, dry-type power transformers such as SC and SCB should be used. Circuit breaker sub-oil, vacuum, SF6 circuit breakers, low oil circuit breakers have the advantages of small size, good performance and large breaking current, etc., and the price is cheap, but the maintenance and repair workload is large and can not be operated frequently. It is not important to apply Power distribution stations or circuits that operate infrequently. The main features of the vacuum circuit breaker are: short contact distance, small size, light weight, small operation power, fast movement, and fire and explosion protection; short arc firing time (usually only half cycle), and the breaking current Irrelevant; after the arc extinguishing, the contact gap media has a fast recovery speed, long service life, low operating noise, frequent operation, and no maintenance. At present, the new product, a permanent magnet high voltage vacuum circuit breaker, is a vacuum circuit breaker using a permanent magnet operating mechanism. Permanent magnet operating mechanism (referred to as "permanent magnet mechanism"), it uses permanent magnets to maintain, electronic control. Compared with the traditional circuit breaker operating mechanism, the permanent magnet mechanism adopts a brand-new working principle and structure. There is only one main moving part during operation, and no mechanical tripping and locking device is needed, so the fault source is small and the reliability is high. Sex, mechanical life up to 100,000 times. The disadvantage of a permanent magnet vacuum circuit breaker is its high price. SF6 circuit breaker has the following advantages: strong breaking capacity, high fracture voltage, allowing more continuous breaking, suitable for frequent operation, low noise, no fire risk, small mechanical and electrical wear, etc., is a kind of excellent performance "No maintenance" breaker. Generally, large-scale transformer substations or loops that frequently operate and have more faults should adopt vacuum circuit breakers and SF6 circuit breakers. 5 Relay protection secondary equipment selection Substation protection relays can be divided into: electromagnetic protection, transistor protection and microcomputer protection. Transistor protection is currently eliminated. Electromagnetic relay protection has been the main protection method of the power supply system in the past, and its main characteristic is that the performance is relatively stable, reliable, and the price is low. The disadvantage is that the area is large and the degree of intelligence is low, and it is inconvenient for the concentration of the upper-level department. Control, scheduling. Microcomputer protection is a digital protection method. It can complete the automatic control and protection of the power distribution and distribution station, and has the functions of monitoring, control, protection, recording, RTU telecontrol terminals, etc. It has a corresponding software platform and can be very convenient. The system is organized to take advantage of the digital protection of communications and achieve remote monitoring. Microcomputer protection systems have been widely used in newly-built transformer substations. In the case of t (Continued on page 159), we should first consider the connection of the power supply or check for power supply problems. After that, we should check the fault code first because it has the self-diagnosis system OBD-n. 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